Melt butter in a saucepan on medium heat. Add sliced mushrooms and sauté 5 minutes. Stir in flour and cook, stirring, for 30 seconds. Gradually whisk in broth and light cream. Cook, stirring constantly, until thickened and gently simmering, 2 to 3 minutes. Combine cornstarch and sherry/wine. Add to pan, along with whipping cream. Simmering, 2 to 4 minutes Stirring occasionally.